Hello,
There is a few glaring issues with this PK. First of all, the officer did hit you with his vehicle, though to his credit you were in the middle of a parking standing there, BUT because of it being a unmarked vehicle, I can see how you may have thought it was a simple civilian rather then it being an officer.
Additionally along those lines with it being a civilian vehicle, the argument could be made that this is somewhat equivalent/similar to the ruling on how detectives can go about PKing in plain clothes (even if this is not a detective)